Angled cut-off in bottom of blow mold

ABSTRACT

MOLD PARTS ARE CLOSED ABOUT A PREFORMED PARISON PINCHING IT SHUT AT ONE END PREPARATORY TO BLOW MOLDING IT TO A HOLLOW ARTICLE. A CUT-OFF BLADE SLIDES WITHIN ONE MOLD PART AT AN ANGLE SO AS TO ENABLE IT TO SEVER THE PARISON AT A POINT ADJACENT THE SEAL LINE OF THE ARTICLE BEING FORMED. THIS ARRANGEMENT ALLOWS PINCHING SHUT PARISONS MADE OF CRYSTALLINE MATERIALS SUCH AS 1-OLEFIN POLYMERS, WHICH PARISONS HAVE BEEN HEATED TO A TEMPERATURE JUST BELOW THE CRYSTALLINE MELTING POINT, IN SUCH A MANNER THAT A GOOD SEAL IS OBTAINED WITH THE SEAL LINE BEING IN AN INDENTED PORTION OF THE BOTTOM; THUS THE BOTTLE WILL SIT FLAT ON A SURFACE.

19, 974 R; D. JOHNSTON 3,793,422

ANGLED CUTEOFF IN BOTTOM OF BLOW MOLD Original Filed Sept. 12, 1969INVENTOR. R. D. JOHNSTON A T TORNE VS United States Patent O ANGLEDCUT-OFF IN BOTTOM OF BLOW MOLD Richard D. Johnston, Bartlesville, Okla.,assignor to Phillips Petroleum Company Original application Sept. 12,1969, Ser. No. 857,420, now

Patent No. 3,632,262, dated Jan. 4, 1972. Divided and this applicationSept. 7, 1971, Ser. No. 178,214 Int. Cl. B29c 17/07, 17/10 US. Cl.264-99 6 Claims ABSTRACT OF THE DISCLOSURE Mold parts are closed about apreformed parison pinching it shut at one end preparatory to blowmolding it to a hollow article. A cut-off blade slides within one moldpart at an angle so as to enable it to sever the parison at a pointadjacent the seal line of the article being formed. This arrangementallows pinching shut parisons made of crystalline materials such asl-olefin polymers, which parisons have been heated to a temperature justbelow the crystalline melting point, in such a manner that a good sealis obtained with the seal line being in an indented portion of thebottom; thus the bottle will sit flat on a surface.

BACKGROUND OF THE INVENTION This is a divisional of my copendingapplication Ser. No. 857,420 filed Sept. 12, 1969, now Patent No.3,632,- 262.

This invention relates to an improved method of sealing and severingparisons of crystalline thermoplastic material preparatory to blowmolding.

The most economical manner for forming parison preforms is tocontinuously extrude a length of tubing and cut it into individualpieces of the proper length. The stretching and forming operation musttake place at a temperature just below the crystalline melting point inorder to take advantage of the molecular orientation effect. Thus, ifthe advantages of molecular orientation are to be achieved along withthe advantages of producing the parisons by continuous extrusion oftubing, as opposed to injection molding a closed end parison, some meansmust be devised to effect a good seal of the parison at this temperatureWhich is below its crystalline melting point. Turner, US. 3,390,426,discloses sealing such parisons by means of multiple pointed membersmoving radially toward a point with a tamping foot within the parisonwhich presses against the closed radial members. From the standpoint ofsimplicity, the ideal arrangement would be simply to close a mold on theparison with a configuration at the bottom of the mold which would sealand sever the parison in a manner similar to that utilized inconventional blow molding. However, since the polymer is at such a lowtemperature that it will not flow, this does not yield a satisfactoryseal.

SUMMARY OF THE INVENTION It is an object of this invention to providefor sealing and severing a crystalline thermoplastic parison atorientation temperature while said parison is in a mold.

According to this invention, mold parts are clamped on atemperature-conditioned parison to seal the walls of said parisontogether at a bottom end of said mold, said thus sealed-off endthereafter being severed from the remainder of said parison by a cut-offmeans in said bottom of said mold, said cut-off means traveling at anangle to a bottom wall-forming surfaces of said mold.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, forming a parthereof, wherein like reference characters denote like parts in thevarious views,

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FIG. 1 is a schematic view of a complete blow molding apparatusutilizing the angled cut-off of the instant invention; FIG. 2 is across-sectional view of the mold parts with the parison held in theclamping means; FIG. 3 is a view similar to FIG. 2 in a later stage ofthe operation; FIG. 4 is a detailed view of the bottom portion of themold parts; FIG. 5 is a perspective view of a bottle molded inaccordance with the instant invention; and FIG. 6 is a perspective viewof the cut-off member as seen from the top.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process and apparatus ofthis invention are applicable for the formation of biaxially orientedhollow thermoplastic articles such as bottles and other containers,toys, lampshades, and other molded products, and the like.

The invention is particularly applicable to the formation of articlesfrom preformed parisons of orientable crystalline thermoplastic resinswhich are heated while in their crystalline state to a temperature justbelow their crystalline melting point, at which temperature molecularorientation and strengthening occurs on stretching. Examples of suitableresins include polymers and copolymers of mono-l-olefins having 2 to 8carbon atoms and the like. Preferred materials are polymers andcopolymers of ethylene, propylene, and l-butene, with polypropylenebeing especially preferred.

These polymers are extruded or molded into parison preforms and thencooled to a temperature below their crystalline freezing point. Theparisons are then heated to an orientation temperature which isgenerally about 1-50 F., preferably 2-20 F., below their crystallinemelting temperature. The crystalline melting point can be determined byheating a sample of the material under a polarizing microscope. Thespecimen is heated slowly and the point at which the last birefringencedisappears is the crystalline melting point.

Following conventional technology, references to crystalline polymersmeans solid polymers normally having a high degree of crystallinity,that is, at least 50 percent, as determined by X-ray analysis orcomparable methods.

In accordance with this invention, the parison walls are sealed by meansof pressing them together from the side by the bottom portions of themold halves as they close. After the walls of the parison have beenpressed together to form a seal, a severing means slides at an anglethrough one of the mold halves to sever the parison, leaving a small tabof the sealed-together parison attached to the article. By having thecut-off mechanism slide at an angle, the mold can be so contoured as toform a recess in the bottom of the bottle so that the tab can projectdownwardly and yet not interfere with the bottle sitting level on a flatsurface.

Referring now to FIG. 1, there is shown a blow molding apparatuscomprising a frame 10. Supported by the frame is an oven 12. Parisons 14are conveyed through this oven by means of a continuous chain 16carrying support pins 18. Heated parisons 14 are lifted off of supportpins 18 by means of a transfer mechanism comprising a pivotal andlaterally reciprocal arm 20. The parisons are grasped by arm 20 at thebottom end thereof, lifted upwardl over the support pin, transferredlaterally to a position under thread-forming jaw 22, and then movedupwardly by means of the extension of cylinder 24, which carriestransfer arm 20. The upper end of parison 14 is thereby positionedwithin thread-forming jaw 22, and this jaw then closes about saidparison to clamp it securely and in so doing, to form the threads in thecase of a bottle. Transfer arm 20 is then withdrawn and the bottom endof parison 14 grasped by means of gripping elements 26 which are alsocarried by frame 10.

Gripping elements 26 hold the bottom end of parison 14 securely asthread-forming jaw 22 raises to thereby stretch and molecularly orientparison 14 in a longitudinal direction. Thread-forming jaw 22 retractsto a position flush with the inner surface of the article-formingcavity, formed by mold halves 28 and 30, as shown in FIG. 3. Mold halves28 and 30 have inserts 32 and 33 designed to form a recess in the bottomof the article being molded. As can be seen from a view of FIGS. 3 and4, as the mold halves close, the parison wall is pinched flat andsqueezed securely together by means of inserts 32 and 33.

After the parison walls have been forced together under pressure toeffect a seal, cut-off member 34 slides at an angle through mold half 30and insert 32 to sever the portion of the parison forming article 36from the scrap portion 38 as shown in FIG. 4. Cut-off member 34 is agenerally flat blade-like member with a pointed edge which abuts againstthe insert member 33 carried by the opposite mold half. It is held in aretracted position by spring 40 and is forced forward by means of aircylinder 42. In FIG. 4, obviously, the process is shown at a later stagefrom that of FIG. 3, at which later stage the parison has been blown outinto conformity with the mold walls. Cut-off member 34 may be actuatedany time after inserts 32 have pressed the walls of the parison togetherto efiect a seal. That is, it ma be actuated before the blow pressurehas been introduced into the parison, or after the blow pressure hasbeen introduced. In either event, the inserts 32 and 33 form a recess inthe bottom of the container so that the small tab 44 will not precludethe article from sitting flat on a level surface.

Cut-off member 34 contacts the portion of mold half 28 represented byinsert 33 at a point spaced downwardly from bottom forming surface 45 adistance of from V to /2 inch, preferably to ,4 inch, to thus form a tabof corresponding length.

Gripping elements 26 can be retracted if desired after the mold closes.Particularly in an alternate embodiment such as is shown in FIG. 3 wherea tamping foot 43 presses against the seal from the inside, this may benecessary to allow some movement of the tail portion as the cut-offmember 34 severs the flattened portion of the parison. Cut-off member 34may completely sever the tail from the remainder of the parison so thatit falls free on opening the mold, or a thin web may connect it to thearticle which has been molded; this web can be easily broken, forinstance, by leaving the gripping elements 26 engaged and moving themrelative to the article.

FIG. shows a perspective view of the bottom of a bottle formed using theinstant invention. Within recess 46 of the resulting container, whichrecess is formed by inserts 32 and 33, there is shown tab 44. Slidingcut-01f member 34 is of a width essentially equal to the length of tab44.

It is essential that sliding cut-off member 34 be positioned at an angleso as to allow the cutting operation to take place ina recessed area;otherwise, the parison would have to be severed exactly flush with thebottom surface of the article, which would be diflicult to do and whichwould result in a weak seal with the type of polymer in question, thatis, a crystalline polymer at a temperature below its crystalline meltingpoint.

It is further essential that the cut-off member 34 be actuated to severthe parison at a time after the molds have closed and sealed the parisontogether by the action of inserts 32 pressing the walls tightlytogether. If the cut-01f member 34 were extended as the mold closes soas to sever the parison as it is being sealed, the portion ,of theparison forming tab 44 would not be pressed together as securely, andtherefore, an inferior seal would result. Here again is a step which iscritical because of the type of material being sealed. In an ordinaryblow molding op- 4 eration involving a molten or tacky parison, thesealing and severing could occur simultaneously and there could be greatleeway in the configuration of the sealing and severing surfaces withoutaffecting the quality of the seal.

It is noted that in this process just described, the mold closes on aportion of the parison which has been stretched. The combination ofhaving the parison stretched prior to closing the mold to seal andactivating cut-off member 34 after the walls have been sealed togetherthat provides an exceptional seal. In this regard, it is noted thatwhile the drawings show the stretching occurring by moving thethread-forming head at the top of the mold initially and to stretch theparison by bringing the means holding the bottom downward. Also, theentire operation could be disposed upside down to that shown, or even ina horizontal plane.

In embodiments where the cut-off member 34 is actuated before theparison is blown out against the mold walls, the parison is preventedfrom retracting by virtue of tab 44 being held between inserts 32 and33, thus eliminating the need for a tamping foot for this purpose.

Many standard parts such as temperature controllers, relays, fittings,and the like have not been shown in the drawings for the sake ofsimplicity, but their inclusion is understood by those skilled in theart and is within the scope of the invention.

EXAMPLE I Propylene homopolymer having a density of 0.905 (ASTM D1505-63T), a melt flow of 2 (ASTM D 1238- 62T, Condition L), and acrystalline melting point of 340 F. Was extruded into tubing having aninternal diameter of 0.8 inch and a wall thickness of 0.125 inch. Thetubing was cooled to room temperature and cut into 7- inch lengths.These 7-inch lengths were heated to a temperature of 320-338 F graspedat a top end by a threadforming means such as means 22 shown in thedrawings and at the bottom end by a gripping element such as element 26shown in the drawings. The parison was then stretched by moving thethread-forming head upward as shown in FIG. 3 of the drawings. Moldsections were then closed as shown in FIG. 3 of the drawings to pinchthe parison shut and seal the Walls along the bottom of the mold. Afterthe mold halves were completely closed, sealing the walls of the parisonshut along a flattened area, a flat blade moving within the mold wall asshown in the figures was actuated to sever the parison so as to separatethe body portion from the tail. Thereafter the blow air was introducedto form the parison against the mold walls thus effectingcircumferential molecular orientation as is shown in FIG. 4. The moldswere opened and the resulting 28-ounce bottle removed. The bottle had atab such as tab 44 shown in the drawing depending from the bottomsurface of the recessed portion of the bottom about of an inch. Thisbottle was found to have a water-tight seal.

EXAMPLE II A number of bottles were made exactly in accordance with thedescription of Example I and tested for a watertight seal. One hundredpercent of the bottles were found to have a water-tight seal.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby, but isintended to cover all changes and modifications within the spirit andscope thereof.

I claim:

1. A process for forming hollow articles comprising: heating anopen-ended hollow parison of a crystalline thermoplastic olefin polymerto a temperature within 150 below a crystalline melting point of saidpolymer; stretching said thus heated parison while at a temperaturebetween 1 and 50 below said crystalline melting point of said olefinpolymer to effect longitudinal molecular orientation; closing a moldabout said heated parison and thereby pressing the walls of said parisontogether at a bottom wall forming end thereof to form a sealed area;thereafter severing said parison at a point within said sealed area soas to separate a tail portion from the remainder of said parison, saidsevering being accomplished at a point so spaced as to leave a tab onsaid remainder of said parison having a length of M to At-inch;introducing blow air to form said parison against said mold thusalfecting circumferential molecular orientation and forming a hollowarticle having a recess in the bottom thereof, said tab being withinsaid recess and shorter than the depth thereof; and removing theresulting article.

2. A method according to claim 1 wherein said severing is elfected at apoint so spaced as to leave a tab of about 4 to ,4 inch.

3. A method according to claim 1 wherein said polymer is heated to atemperature of 220 below the crystalline melting point in an air ovenprior to stretching.

4. A method according to claim 1 wherein said polymer is a polymer of atleast one mono-l-olefin having 2-8 carbon atoms per molecule.

5. A method according to claim 1 wherein said olefin 6 polymer ispolypropylene and wherein said polypropylene is heated to a temperatureof 320-338 F. prior to said stretching.

6. A method according to claim 5 wherein said sealed area is flat andsaid parison is at a temperature of 320 338 F. during said stretching.

References Cited UNITED STATES PATENTS 3,592,885 7/1971 Goins et al.264-94X FOREIGN PATENTS 911,228 11/ 1962 Great Britain 264--98 957,0104/1964 Great Britain 264-161 J EFFERY R. THU RLOW, Primary Examiner I H.SILBAUGH, Assistant Examiner US. Cl. X.R.

